attribute_forms

A bare attribute name after @ denotes a true flag or render keyword.
A negated flag uses a trailing bang after the attribute name.
A valued attribute uses a space after the attribute name followed by a value.
A colon after the attribute name is optional legacy syntax and is not part of the value.
Common attributes include plan, status, priority, criticality, confirmation, owner, log, tags, and references with the @ prefix.
Any custom attribute name is allowed.

Interactive page: attribute_forms